A factor that effects a vehicle's fuel efficiency is the load experienced by the engine. If the engine experiences a high load, or runs at high revolutions per minute, fuel efficiency typically is reduced. On the other hand, if the engine is unloaded, or runs at a relatively lower number of revolutions per minute, the fuel efficiency commonly improves.
The load experienced by the engine may be directly related to the associated gear ratio in which the transmission is operating. Too high a numerical gear ratio may cause the engine to run too fast and fail to operate at a desired level of fuel efficiency. Conversely, an extremely low numerical gear ratio may adversely affect vehicle performance characteristics, including acceleration and ease of operation. Accordingly, communication between the engine and the transmission in determining the load experienced by the engine and determining a desired or proper gear ratio can improve fuel efficiency.